1. Field of the Invention
The present invention relates to a novel hot melt composition excellent in adhesive property. More particularly, it relates to a hot melt composition which is solid at ambient temperature and may be melted by heating to be applied on various materials and then solidified by cooling to adhere onto materials for serving as an adhesive or coating composition.
2. Prior Art
The commonly used matrix polymers for the hot melt compositions are polyethylene base copolymers such as ethylene-vinyl acetate copolymers and ethylene-acrylate copolymers and thermoplastic polymers such as polyethylene, polyamides, polyurethanes and polyesters, to which a variety of waxes as a viscosity adjusting agent and a tackifying resin are blended.
Natural resins such as rosin and rosin esters have been widely used as the prior art tackifying resins. Among them, rosin esters are recommended because of their excellent tackifying properties. However, such natural resins are unstable in cost and supply. For this reason, there is an increasing tendency of using petroleum resins in place of the rosin esters in recent years. However, petroleum resins have various disadvantages, particularly they are poor in tackifying and heat resistant properties. Although many proposals have been made to eliminate the disadvantages mentioned above, any petroleum resin having satisfactory properties has not yet been produced. It has been tried to hydrogenate petroleum resins for improving hues and heat resistant properties thereof. For example, those obtained by completely hydrogenating aromatic petroleum resins or cyclopentadiene base resins have been widely used. However, the tackifying properties of such resins are extremely poor. In order to improve such properties, it has been already proposed to partially hydrogenate an aromatic petroeum resin such that 5 to 80% of the aromatic components thereof are hydrogenated at the intranuclear positions, i.e. to hydrogenate the aromatic rings of the resin. (See Japanese Patent Publication No. 31899/'77) However, the tackifying properties of the thus modified resin is not satisfactorily improved so much as adapted for broad uses when compared to rosin esters of natural resources. Another proposal has been made to use a resin produced by the steps of copolymerizing a cyclopentadiene base monomer with a monovinyl substituted aromatic hydrocarbon such as styrene, .alpha.-methylstyrene or vinyltoluene and then partially hydrogenating the resultant copolymer such that 0 to 80% of the aromatic rings are hydrogenated. (See Unexamined Japanese Patent Publication No. 14059/'77) However, this prior art resin has disadvantages that the miscibility thereof with waxes is unsatisfactory and that the adhesive properties thereof to some materials including plastics is unsatisfactory. A further proposal known to the art is utilization of a hydrogenated copolymer of a cyclopentadiene base monomer and an ethylenic unsaturated ester. (See Unexamined Japanese Patent Publication No. 70450/'75) However, this known hydrogenated copolymer is disadvantageous in that it emits intensely an offensive odor when heating to melt the same with a ethylene-vinylacetate copolymer and/or a wax to prepare a hot melt composition, since a vinylacetate monomer, methylmethacrylate or the like is used as the starting material. Unexamined Japanese Patent Publication No. 132060/'75 discloses yet a further proposal wherein a hydrogenation product of a copolymer of a cyclopentadiene base monomer is copolymerized with a polar vinyl compound and a polar vinylidene compound, the amount of said polar vinyl compound being so large as 10 to 60 wt.%, resulting in insufficient miscibility with waxes. Moreover, the tackifying properties of the last mentioned product is far from satisfactory.